add hydra project declaration

hydra-project.nix

@@ -0,0 +1,27 @@
+{ pkgs ? import <nixpkgs> {}}:
+{
+  jobsets = pkgs.runCommand "spec.json" {}
+    ''
+    cat > $out << EOF
+    {
+        "main": {
+            "enabled": 1,
+            "hidden": false,
+            "description": "js",
+            "nixexprinput": "nixScripts",
+            "nixexprpath": "main.nix",
+            "checkinterval": 300,
+            "schedulingshares": 10,
+            "enableemail": false,
+            "emailoverride": "",
+            "keepnr": 10,
+            "inputs": {
+                "nixScripts": { "type": "git", "value": "git://github.com/m-labs/nix-scripts.git", "emailresponsible": false },
+                "nixpkgs": { "type": "git", "value": "git://github.com/NixOS/nixpkgs-channels nixos-18.09", "emailresponsible": false },
+                "artiqSrc": { "type": "git", "value": "git://github.com/m-labs/artiq.git master 1", "emailresponsible": false }
+            }
+        }
+    }
+    EOF
+    '';
+}